This invention relates generally to improvements in fluid transfer pipe systems, particularly of the type used for transferring liquid fuel from an underground storage tank to one or more dispensing pumps. More specifically, this invention relates to an improved multiaxial fluid transfer pipe system adapted for facilitated installation and improved operational performance with respect to liquid fuel dispensing concurrently with recovery and recirculation of fuel vapors.
Pipe systems and networks for use in transferring liquid fuel from an underground fuel storage tank to an above-ground dispensing pump are well-known in the art, particularly in the context of automobile service stations. In this regard, the liquid fuel such as gasoline is traditionally stored in an underground fuel storage tank in convenient proximity to one or more dispensing pumps. The storage tank and the dispensing pump normally include suitable shut-off valve devices located within a shallow sump for easy access by service station personnel. The transfer pipe system is normally installed underground in a position connected between the tank and pump sumps for fuel transfer and dispensing when the pump is operated.
In the past, buried fuel storage tanks and transfer pipe systems associated therewith were constructed from convenient and relatively inexpensive materials such as steel plate, iron piping, etc. However, these iron-based materials were subject to corrosion, resulting in eventual failure of the storage tank and/or the related transfer pipe system. Such failures unfortunately resulted in leakage of the liquid fuel into the surrounding soil, creating a substantial risk of ground water contamination.
In recent years, new and improved fuel storage tanks and related pipe systems have been constructed from noncorrosive materials, such as fiberglass and the like. In such installations, a primary fuel transfer pipe or conduit is commonly mounted within an outer containment conduit to provide a double-walled construction intended to further reduce the risk of fuel leakage. Unfortunately, a double-walled pipe system of this type requires a complex assembly of pipe components and fittings which are assembled piecemeal by means of a large number of threaded or adhesively joined connectors, resulting in a piping network which is both difficult and costly to install.
In addition, governmental air quality regulations now frequently require a vapor recovery system to prevent escape of excessive fuel vapors to the air when fuel is dispensed. The vapor recovery system normally comprises a separate flow line associated with a vacuum pump to draw fuel vapor from a dispensing nozzle to the underground fuel storage tank for recondensation. The inclusion of the vapor recovery line, which is also formed from assembled pipe components and fittings of preferably noncorrosive material, further increases the overall cost and complexity of the fuel transfer pipe network. Moreover, a portion of the recirculated fuel vapor tends to recondense within the vapor recovery line, whereby the inclination angle of the installed vapor recovery line must be carefully controlled to prevent vapor lock. In addition, the vapor recovery line provides a separate fuel leakage site in the event of line failure.
There exists, therefore, a significant need for improvements in fuel transfer pipe systems of the type used in a fuel transfer and dispensing environment. There exists a particular need for a simplified pipe system having a primary fuel flow line and a vapor recovery line adapted for simplified and easy installation within a protective outer containment conduit. The present invention fulfills these needs and provides further related advantages.